Skip all changes in this file
git add --patch gives you the opportunity to make a decision on every code change in all files individually, providing you a menu that looks like this:
Stage this hunk [y,n,q,a,d,/,j,J,g,e,?]?
Option d is
d - do not stage this hunk or any of the later hunks in the file
This comes in handy when there is a host of whitespace changes in a file that you don't want to commit. Just hit d to skip all those whitespace changes and go to the next file.